In radio communication networks, such as telecommunication networks, efforts have been made to offer seamless wireless communications services essentially everywhere.
This has been achieved by providing so called macro cells, which for many applications often provide acceptable service coverage and quality. Nevertheless, some areas such as important and/or very populated buildings are subject to other, more specialized, solutions. In some areas, the use of macro cells is insufficient, i.e. service coverage and quality is insufficient. Furthermore, it is not economically viable to consider other, more specialized solutions. Hence, there is a need for another solution to provide acceptable service coverage and quality in these areas, which may be underground garages, tunnels, apartment flats, subways and more.
One solution in such cases is to deploy repeaters. Essentially, the radio signals are received at one antenna and forwarded at another, possibly after some amplification. A related solution is to deploy relays, in which radio signals are decoded to extract a message. Then the message is coded and forwarded, possibly after some amplification. In both solutions, a mobile terminal is connected to a cell, but via a repeater or a relay. The cell is served by a radio base station, comprised in, for example, a telecommunication network.
In the following a short comparison between repeaters and relays is presented. First, repeaters forwards (and optionally amplifies) the radio signals and any noise present. This usually has a negative impact on the donor cell. All received radio signals at the pick-up antenna are repeated. The repeater can not select which radio signals to forward. Hence, the repeater need not have any knowledge about the communication protocols of the radio signals being forwarded. Next, relays forwards regenerated radio signals and it can be selective when forwarding radio signals. Since the radio signals are regenerated the regenerated signal may comprise less noise. However, the relay has to comply with the radio communications protocols of the radio signals being forwarded.
A problem with repeaters/relays is that they can make a mobile terminal contribute to the received signal at a base station antenna at higher levels than desired. For example, the repeater/relay may amplify with a high gain, and the mobile terminal may transmit at its minimum power level. This may jeopardize the stability of the system and the quality of service for other connections. Moreover, repeaters/relays may be active on a regular basis, also when not activated by a mobile terminal. This leads to unnecessary energy consumption.
Radio communication networks are typically separated into Radio Access Network (RAN) and Core Network, comprising a core network node. The signalling between the mobile terminal and the radio access network is referred to as the Access Stratum (AS), while the signalling between the mobile terminal and the core network node is referred to as the Non-Access Stratum (NAS). These NAS message are carried in container messages, typically referred to as Direct Transfer messages, between the mobile and the radio access network, such as base stations, radio network controllers etc. The radio access network, forwards NAS messages from the mobile terminal to the designated core network node. Each radio base station broadcasts information about the connected core network to mobile terminals. This information is used to tag the NAS message with information about the intended core network node, such as the expected core network type, the intended public land mobile network, encryption information and more. The actual NAS message part of the broadcasted information is a bit string that may be interpreted by the receiving core network node.